An Amtrak train travels northbound from 30th Street Station, Monday, May 18, 2015 in Philadelphia. Amtrak's Northeast Corridor trains resumed service Monday following last week's deadly derailment that killed eight people and injured more than 200 others. Photo Credit: AP

PHILADELPHIA - Amtrak trains began rolling again between Philadelphia and New York early Monday, the first time since a train derailment almost a week ago killed eight people and injured more than 200 others.

Amtrak resumed service along the corridor with a 5:30 a.m. southbound train leaving New York City. The first northbound train, scheduled to leave Philadelphia at 5:53 a.m., was delayed and pulled out of 30th Street Station at 6:07 a.m. Both trains arrived at their destinations about 30 minutes behind schedule.

All Acela Express, Northeast Regional and other services also resumed.

Amtrak officials said Sunday that trains along the Northeast Corridor from Washington to Boston would return to service in "complete compliance" with federal safety orders following last week's deadly derailment.

Amtrak President Joseph Boardman said staff and crew worked around the clock to restore service.

"It's great to be back," said Christian Milton of Philadelphia. "I've never had any real problems with Amtrak. I've been traveling it for over 10 years. There's one accident in 10 years. Something invariably is going to happen somewhere along the lines. I'm not worried about it."

"My biggest takeaway was the under-promise and over-deliver, and the surprise of having it come back this morning when that wasn't expected," Carberry said. "That was a good thing for Amtrak."

At New York City's Penn Station early Monday, police with dogs flanked the escalator as a smattering of passengers showed their tickets to a broadly smiling Amtrak agent and headed down to the platform.

Investigators with the National Transportation Safety Board have focused on the acceleration of the train as it approached the curve, finally reaching 106 mph as it entered the 50-mph stretch north of central Philadelphia and only managing to slow down slightly before the crash.

The Amtrak engineer, who was among those injured in the crash, has told authorities that he does not recall anything in the few minutes before it happened. Characterizing engineer Brandon Bostian as extremely safety conscious, a close friend said he believed reports of something striking the windshield were proof that the crash was "not his fault."

"He's the one you'd want to be your engineer. There's none safer," James Weir of Burlison, Tennessee, told The Associated Press in a telephone interview on Sunday.

Investigators also have been looking into reports that the windshield of the train may have been struck by some sort of object, but NTSB member Robert Sumwalt said on CBS's "Face the Nation" program Sunday that he wanted to "downplay" the idea that damage to the windshield might have come from someone firing a shot at the train.

"I've seen the fracture pattern; it looks like something about the size of a grapefruit, if you will, and it did not even penetrate the entire windshield," Sumwalt said.

Officials said an assistant conductor on the derailed train said she heard the Amtrak engineer talking with a regional train engineer and both said their trains had been hit by objects. But Sumwalt said the regional train engineer recalls no such conversation, and investigators had listened to the dispatch tape and heard no communications from the Amtrak engineer to the dispatch center to say that something had struck the train.